Vibration reduced x-ray anode

ABSTRACT

An x-ray tube of the rotating anode type comprising a rotor and bearing assembly including a rotatable rotor shaft which is connected to and supports an anode assembly for rotation therewith, the interconnected parts of the rotor and anode assemblies being substantially matched as to thermal conductivity, expansion, and yield strength at elevated temperatures and low vapor pressures, thus providing improved resistance to system imbalance which is incurred during processing and operation of the tube.

Unite States Patent Langer et al.

[ Dec. 17, 1974 VIBRATION REDUCED X-RAY ANODE Inventors: Helmut Langer,Springdale; Vincent Sollima, Stamford, both of Conn.

Assignee: The Machlett Laboratories,

Incorporated, Springdale, Conn.

Filed: Nov. 19, 1973 App]. No.: 417,464

3,710,162 l/l973 Bougle 313/60 Primary Examiner-John Kominski AssistantExaminer-Darwin R. Hostetter Attorney, Agent, or FirmI-Iarold A. Murphy;Joseph D. Pannone; John T. Meaney [57] ABSTRACT An x-ray tube of therotating anode type comprising a rotor and bearing assembly including arotatable rotor shaft which is connected to and supports an anodeassembly for rotation therewith, the interconnected parts of the rotorand anode assemblies being substantially matched as to thermalconductivity, expansion, and yield strength at elevated temperatures andlow vapor pressures, thus providing improved resistance to systemimbalance which is incurred during processing and operation of the tube.

5 Claims, 2 Drawing Figures I if ease s YIII, III

VIBRATION REDUCED X-RAY ANODE BACKGROUND OF THE INVENTION In an x-raytube of the rotating anode type, imbalance of components is undesirableand detrimental. Operation of an imbalanced rotor-anode structure insuch a tube leads to many undesirable factors, in particular excessivenoise and vibration and production of poorly defined focal spots, andoften results in premature failure of the x-ray tube. In addition, someof these factors, such as noise and vibration, often cause discomfort inpatients.

Although in the manufacture of x-ray tubes the rotating anode and rotorassemblies undergo a balancing operation prior to assembly, in laterstages of tube processing and subsequent heating of all components ofthe device, and during actual operation of the x-ray tube, expansiondifferences, deformation of mounting components, etc., cause imbalance,with the result that vibration and noise levels show an undesirable andsometimes marked increase.

In normal practice the anode-rotor assembly is secured to the tubebearing system by means of screws which are tightened to a predeterminedtorque and are often secured in a manner which should eliminateloosening during heat processing. However, in actual application,certain mechanical changes, caused by yielding, take place and result inimbalance and high displacement levels.

SUMMARY OF THE INVENTION In accordance with this invention, a greatlyimproved bearing-target system for rotating anode x-ray tubes has beenachieved by forming interconnecting portions of the system of materialswhich are substantially matched to possess low thermal conductivity, lowthermal expansion, and high yield strength at elevated temperature andlow vapor pressures. It has been found and demonstrated that materialsof the iron-nickelcobalt family or alloys thereof when used for thetarget nosepiece, the rotor plug, the bearing nailhead, and the mountingscrews, will result in greatly reduced dis placement levels during allthermal processing of an x-ray tube.

Typically, with this invention displacement levels are decreased by anaverage of about db and the system remains at a well-balanced stateduring the operational life of the tube.

In a typical construction of an x-ray tube targetrotor-bearing assemblyembodying this invention the nosepiece is made from a high melting pointrefractory metal, preferably molybdenum or an alloy thereof such as TZM(titanium-zirconium-molybdenum alloy containing about 99.5% molybdenum).The nosepiece is brazed to the rotor plug, which plug is made of Fe-Ni-Co alloy as are the bearing nailhead and the mounting screws by whichthe rotor plug is secured to the bearing nailhead.

Rotating anode x-ray tubes having target-rotorbearing assemblies madewith such matched components have shown consistently lower vibration andnoise levels, both after heat processing and during operational life.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objectives of thisinvention will become apparent from the following description, taken inconnection with the accompanying drawings, wherein FIG. 1 is a sideelevational view partly in axial section of an x-ray tube embodying theinvention; and

FIG. 2 is an enlarged axial sectional view of the interconnectedanode-rotor-bearing assembly of the tube shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly tothe drawings, there is shown in FIG. 1 a rotating anode x-ray tube 10which includes an evacuated envelope 12 having a bulb portion 14 at oneend and a reduced diameter elongated neck portion 16 at its other end.

Within the envelope bulb portion 14 is an electronemitting cathode 18which is fixed by a plate 20 to one end of the cathode support 22.Support 22 is sealed to the envelope in a hermetic fashion and from itextend leads 24 whereby the filament or filaments (not shown) in thecathode structure are connected to an external source of filament power.The cathode and its supporting structure are not shown and described indetail since they may be conventional in construction and do not inthemselves constitute an important part of this invention.

The cathode 18 is located so that in operation it will direct a beam ofelectrons onto an inclined edge portion 26 of a disclike anode target28. In operation of the tube, the target 28 is made to rotate about itsaxis so as to constantly present a new surface to the electron beam fromthe cathode 18. In the normal operation of a tube of this type,electrons impinging upon the surface 26 will cause the generation ofx-rays which will pass out of the tube through the adjacent side wall ofthe envelope.

For rotation of the target 28 there is provided a shaft 30 which extendslongitudinally within the envelope neck portion 16, which shaft 30 isrotated by inductive means (not shown) located in encircling relation tothe envelope neck portion 16. Shaft 30 is mounted by ball bearing units32 within a fixed hollow cylindrical axially extending support member 34which is sealed at its lower end by a collar 36 to a reentrant endportion 38 of the envelope neck portion 16. A tubular spacer 40 extendsbetween the outer bearing races for location purposes. The lower innerend of the bore within the support 34 is provided with a circumferentialledge 42 upon which the lower bearing outer race rests, and a set screw44 in an upper end portion of the support 34 engages the upper edge ofthe upper bearing outer race for retaining the assembly in place.

Encircling the support 34 in spaced relation therewith is a rotor skirt46 which is secured at its upper end to a rotor plug 48. Rotor plug 48is attached by mounting screws 50 to a bearing nailhead" 52. Nailhead 52is a ring-shaped element which is rigidly fixed as by brazing to areduced upper end portion 54 of the bearing shaft 30.

A connecting member or nosepiece 56 has a flanged lower end which isfitted into and closely embraced by the rotor plug 48, and is brazedthereto. The other end of the nosepiece 56 extends through a hole in thecenter of the target 28, with an enlarged flange portion 58 thereofproviding a seat upon which the target rests. The adjacent end of thenosepiece extends above the target surface and is threaded to receive anut 60 by means of which the target 28 is firmly held against the flangeportion 58. The nosepiece 56 is preferably provided with a central bore62 to reduce material and thereby provide a heat dam, thus reducingconductivity of heat downward through the structure and into thebearings.

It will be understood that when inductive forces act upon the rotorstructure, rotation thereof results. By this means the target can berotated at high speeds such as 10000 rpm, for example.

Conventionally the nosepiece 56 is made of molybdenum, the nailhead 52is made of stainless steel, the rotor plug 48 is made of Kovar, and thescrews 50 are made of stainless steel. In some older devices thenosepiece 56 is made of molybdenum while the nailhead 52 is made ofstainless steel, and the rotor plug 48 and screws 50 are made of iron.When such conventional and older devices were rotated at high speedssuch as 10,000 rpm, for example, it was found that extremely undesirablevibration levels were reached, with consequent noise, especially whenthe parts of the devices assumed relatively high operating temperatures.

In accordance with this invention, it has been found that such vibrationand resultant noise may be reduced by as much as five decibels by makingthe nosepiece 56, rotor plug 48, nailhead 52 and screws 50 of materialswhich are relatively closely matched to possess low thermalconductivity, low thermal expansion, and high yield strength at elevatedtemperatures and low vapor pressures. Such a material is theiron-nickel-cobalt family. It has been found that TZM may be used as thematerial for the nosepiece 56 while Kovar may be used Present InventionPart Material Exp. Coefficient Nosepiece 56 TZM Sl X lO' /oC Rotor Plug48 Kovar 79 X l /oC Nailhead 52 Kovar 79 X l0"/0C Screws 50 Kovar 79 Xl0' /oC From the above chart it will be seen that all four components ofthe structure have good thermal matching. Additionally, Kovar alsoprovides lowered heat conductivity, thereby achieving a cooler bearingsystem.

Assemblies of prior construction have an average of about five decibelsgreater displacement levels and upon becoming heated become imbalanced.Such prior assemblies also tend to increase in vibration amplitudesduring the operational life of the x-ray tube, believed to be caused bycomprising unmatched components.

The following chart illustrates in a conventional structure the linearexpansion coefficient for the referred-to components in a temperaturerange of about from 30-600C:

Conventional Structure Linear expansion coefficients in another olderstructure in the same temperature range are illustrated in the followingchart:

Older Structure Part Material Exp. Coefficient Nosepiece 56 Molybdenum51 X l0' /oC Rotor Plug 48 lron 13] X lO /oC Nailhead 52 Stainless Steell X l0"/oC Screws 50 lron 131 X l0"/0C From the foregoing it will beunderstood that in accordance with the teachings of this invention animproved x-ray tube structure has been achieved by making several of thecomponent parts thereof of materials matched as to several physicalproperties whereby system imbalance is greatly reduced by reduction indifferential thermal expansion when the tube components are heatedduring tube processing and during actual operation of the tube.

It will be understood, however, that various modifications and changesmay be made by those skilled in the art without departing from thespirit of the invention as expressed in the accompanying claims.Accordingly, all matter shown and described is to be interpreted asillustrative and not in a limiting sense.

We claim:

1. An x-ray tube comprising an envelope containing a rigid anodesupporting structure, a rotor structur rotatably mounted on saidsupporting structure, and an anode structure having a portion engagingand secured to a portion of said rotor structure for rotation therewith,said portion of said anode structure being titanium-zirconium-molybdenumalloy containing about 99.5% molybdenum, and the engaged portion of therotor structure being of material in the Fe-Ni-Co family.

2. An x-ray tube of the rotating anode type comprising an evacuatedenvelope containing a fixed supporting structure, a rotatable shaftwithin said supporting structure, bearings between said shaft andsupporting structure, a portion of said shaft extending beyond one endof the supporting structure, a rotor structure including a portionsecured to said portion of the shaft for rotation therewith, and ananode structure including a portion secured to said rotor structure,said portion of the anode structure being oftitanium-zirconium-molybdenum alloy containing about 99.5% molybdenumand the rotor structure and shaft being of materials in the Fe-Ni-Cofamily.

3. An x-ray tube of the rotating anode type comprising an evacuatedenvelope containing a hollow axially extending target support fixed atone end to said envelope, a shaft extending axially within said supportand having one end extending beyond the adjacent end of the support,bearings rotatable mounting said shaft in said support, a nailhead onsaid end of the shaft, a rotor structure mounted on said shaft forrotation therewith 4. An x-ray tube as set forth in claim 3 wherein thematerial of said nosepiece is titanium-zirconiummolybdenum alloycontaining about 99.5% molybdenum, and the material of said rotor plugand nailhead is Fe-Ni-Co alloy.

5. An x-ray tube as set forth in claim 3 wherein said rotor plug issecured to the nailhead by screws of Fe- Ni-Co alloy.

1. AN X-RAY TUBE COMPRISING AN ENVELOPE CONTAINING A RIGID ANODESUPPORTING STRUCTURE, A ROTOR STRUCTURE ROTATABLY MOUNTED ON SAIDSUPPORTED STRUCTURE, AND AN ANODE STRUCTURE HAVING A PORTION ENGAGINGAND SECURED TO A PORTION OF SAID ROTOR STRUCTURE FOR ROTATION THEREWITH,SAID PORTION OF SAID ANODE STRUCTURE BEING TITANIUM-ZIRCONIUM-MOLYBDENUMALLOY CONTAINING ABOUT 99.5% MOLYBDENUM, AND THE ENGAGE PORTION OF THEROTOR STRUCTURE BEING OF MATERIAL IN THE FE-NI-CO FAMILY.
 2. An x-raytube of the rotating anode type comprising an evacuated envelopecontaining a fixed supporting structure, a rotatable shaft within saidsupporting structure, bearings between said shaft and supportingstructure, a portion of said shaft extending beyond one end of thesupporting structure, a rotor structure including a portion secured tosaid portion of the shaft for rotation therewith, and an anode structureincluding a portion secured to said rotor structure, said portion of theanode structure being of titanium-zirconium-molybdenum alloy containingabout 99.5% molybdenum and the rotor structure and shaft being ofmaterials in the Fe-Ni-Co family.
 3. An x-ray tube of the rotating anodetype comprising an evacuated envelope containing a hollow axiallyextending target support fixed at one end to said envelope, a shaftextending axially within said support and having one end extendingbeyond the adjacent end of the support, bearings rotatable mounting saidshaft in said support, a nailhead on said end of the shaft, a rotorstructure mounted on said shaft for rotation therewith comprising arotor plug secured to said nailhead and a rotor skirt connected at oneend to said plug and encircling said support, and a target structureattached to said rotor structure for rotation therewith comprising atarget disc and a nosepiece connecting said disc to said rotor plug,said nosepiece being of titanium-zirconium-molybdenum alloy containingabout 99.5% molybdenum and said rotor plug and nailhead being ofFe-Ni-Co alloy.
 4. An x-ray tube as set forth in claim 3 wherein thematerial of said nosepiece is titanium-zirconium-molybdenum alloycontaining about 99.5% molybdenum, and the material of said rotor plugand nailhead is Fe-Ni-Co alloy.
 5. An x-ray tube as set forth in claim 3wherein said rotor plug is secured to the nailhead by screws of Fe-Ni-Coalloy.